is the internal motion that takes place in man, which is called his
INTELLECTUAL FACULTIES, his THOUGHTS, his PASSIONS, his will. Of these
we have no other mode of judging, than by their action; that is, by
those sensible effects which either accompany or follow them. Thus, when
we see a man run away, we judge him to be interiorly actuated by the
passion of fear.

Motion, whether visible or concealed, is styled ACQUIRED, when it is
impressed on one body by another; either by a cause to which we are a
stranger, or by an exterior agent which our senses enable us to
discover. Thus we call that _acquired motion_, which the wind gives to
the sails of a ship. That motion which is excited in a body, that
contains within itself the causes of those changes we see it undergo, is
called SPONTANEOUS. Then it is said, this body acts or moves by its own
peculiar energies. Of this kind is the motion of the man who walks, who
talks, who thinks. Nevertheless, if we examine the matter a little
closer, we shall be convinced, that, strictly speaking, there is no such
thing as spontaneous motion in any of the various bodies of Nature;
seeing they are perpetually acting one upon the other; that all their
changes are to be attributed to the causes, either visible or concealed,
by which they are moved. The will of man is secretly moved or determined
by some exterior cause that produces a change in him: we believe he
moves of himself, because we neither see the cause that determined him,
the mode in which it acted, nor the organ that it put in motion.

That is called SIMPLE MOTION, which is excited in a body by a single
cause. COMPOUND MOTION, that which is produced by two or more different
causes; whether these causes are equal or unequal, conspiring
differently, acting together or in succession, known or unknown.